Method of operating a hearing device and a hearing device

ABSTRACT

A method of operating a hearing device is disclosed, the method comprising the steps of:
         sensing an acoustic signal and providing an input acoustic signal,   sensing a magnetic signal and providing a input magnetic signal,   selecting one of the input acoustic signal and the input magnetic signal as an information signal, wherein the input magnetic signal or the input acoustic signal is selected as the information signal after a signal detection process has determined a probability being above a preset value, said probability being indicative of a presence of audio information in the input magnetic signal or the input acoustic signal, respectively, and   processing the information signal and providing an output signal to a user of the hearing device.       

     In addition, corresponding hearing devices are also disclosed.

The present invention is directed to a method of operating a hearingdevice as well as to a hearing device.

Automatic telephone detection allows a hearing device to switch to anappropriate hearing program when a telephone conversation is detected.

Currently, the telephone conversation is detected by monitoring a signaltransmitted via a so-called T-coil. If a magnetic field sensed by theT-coil is high enough a trigger is activated. Most telephones however donot produce a strong enough magnetic field by themselves. A commonsolution is therefore to attach an additional magnet to the telephonewhich is then used to trigger the T-Coil signal detector. In U.S. Pat.No. 6,633,645 and U.S. Pat. No. 6,760,457, a known hearing device isdescribed having a magnetic sensor for detecting a magnetic field closeto the hearing device. The output of the magnetic sensor is used toswitch the hearing device to a telephone mode, in which a specifichearing program is activated.

Recently more sensitive detection devices have been introduced thatoften work without additional magnets. However, these detection devicesare still not very reliable.

For example, U.S. Pat. No. 7,010,132 describes a hearing device thatanalyses the signal output of a magnetic field detector to determinewhether an acoustic signal is present in the magnetic field.

This solution is generally not very desirable as it requires the user tomodify the telephone.

Furthermore, U.S. Pat. No. 7,016,510 describes a method for switching ahearing device to a telephone mode based on two hearing devices worn onthe left and on the right side. A signal from one hearing device iscompared to a signal from the other hearing device and a decision isbased on the difference between the two signals. This solution does onlywork if two hearing devices are present.

An object of the present invention is therefore to provide a method foroperating a hearing device that is very reliable and simple toimplement, in particular without the need to adapt the hardware of thehearing device.

This and other objects have been reached by the features of claim 1.Advantageous embodiments of the present invention as well as a hearingdevice are given in further claims.

The present invention is directed to a method of operating a hearingdevice, the method comprising the steps of:

-   -   sensing an acoustic signal and providing an input acoustic        signal,    -   sensing a magnetic signal and providing a input magnetic signal,    -   selecting one of the input acoustic signal and the input        magnetic signal as an information signal, wherein the input        magnetic signal is selected as the information signal after a        signal detection process has determined a probability being        above a preset value, said probability being indicative of a        presence of audio information in the input magnetic signal, and    -   processing the information signal and providing an output signal        to a user of the hearing device.

Furthermore, the present invention is also directed to a method ofoperating a hearing device, the method comprising the steps of:

-   -   sensing an acoustic signal and providing an input acoustic        signal,    -   sensing a magnetic signal and providing a input magnetic signal,    -   selecting one of the input acoustic signal and the input        magnetic signal as an information signal, wherein the input        acoustic signal is selected as the information signal after a        signal detection process has determined a probability being        above a preset value, said probability being indicative of a        presence of audio information in the input acoustic signal, and    -   processing the information signal and providing an output signal        to a user of the hearing device.

Embodiments of the present invention further comprise the step ofdetermining the probability using at least one of the followingcriterions:

-   -   a bandwidth of the input magnetic signal is below a predefined        value, in particular below 3 kHz;    -   a bandwidth of the input acoustic signal is below a predefined        value, in particular below 3 kHz;    -   a telephone dial tone has been detected;    -   a behavior of a feedback canceller filter is due to an object        being close to an ear;    -   a magnetic field is detected in a T-coil.

In further embodiments of the present invention, the step of selectingone of the input acoustic signal and the input magnetic signal as theinformation signal is using a state machine.

In other embodiments, the state machine comprises at least four statescomprising:

-   -   an Idle state being a default state;    -   an DialTone state being representative for detecting dial tone;    -   a Listen state being representative for receiving acoustic        information from a remote person talking via telephone;    -   a Speak state being representative for speaking to a remote        person via telephone.

The present invention is also directed to a hearing device comprising:

-   -   an acoustic sensor for sensing an acoustic signal and providing        an input acoustic signal,    -   a magnetic sensor for sensing a magnetic field signal and        providing an input magnetic signal,    -   a telephone detection unit connected to the magnetic sensor for        selecting one of the input acoustic signal and the input        magnetic signal as an information signal, wherein the telephone        detector unit selects the input magnetic signal as the        information signal after a telephone detection process has        determined a probability being above a preset value, said        probability being indicative of a presence of audio information        in the input magnetic signal, and    -   an information processing unit (8) for processing the        information signal to a user of the hearing device.

Furthermore, the present invention is also directed to a further hearingdevice comprising:

-   -   an acoustic sensor for sensing an acoustic signal and providing        an input acoustic signal,    -   a magnetic sensor for sensing a magnetic field signal and        providing an input magnetic signal,    -   a telephone detection unit connected to the acoustic sensor for        selecting one of the input acoustic signal and the input        magnetic signal as an information signal, wherein the telephone        detector unit selects the input magnetic signal as the        information signal after a telephone detection process has        determined a probability being above a preset value, said        probability being indicative of a presence of audio information        in the input magnetic signal, and    -   an information processing unit for processing the information        signal to a user of the hearing device.

In further embodiments of the present invention, the hearing devicefurther comprises a switch unit for operationally connecting either themagnetic sensor or the acoustic sensor to the information processingunit, the switch unit being controllable by the telephone detectionunit.

In further embodiments of the present invention, the hearing devicefurther comprises a state machine in the telephone detection unit.

In still further embodiments of the present invention, the state machinecomprises at least four states comprising:

-   -   an Idle state being a default state;    -   an DialTone state being representative for detecting dial tone;    -   a Listen state being representative for receiving acoustic        information from a remote person talking via telephone; and    -   a Speak state being representative for speaking to a remote        person via telephone.

This invention enables a hearing device to recognize when the user istalking on the phone using mainly acoustic features. No additionalhardware is necessary in the hearing device. This is desirable, as anyhardware components will take up space and increase the powerconsumption of the hearing device. A software based solution is highlypreferred. The traditional T-Coil (or an equivalent device) cancontribute to the detection, but is not essential.

A preferred solution as described here does not require any hardwaremodification of neither telephone nor hearing aid.

The present invention will be further described by referring to drawingsshowing exemplified embodiments of the present invention.

FIG. 1 shows an overview of a signal flow for a telephone detectionsystem according to the present invention;

FIG. 2 shows a diagram of a state machine implemented in a hearingdevice;

FIG. 3 shows a hearing device according to the present invention.

FIG. 1 shows a signal flow for a telephone detection system that isimplemented in a hearing device. The telephone detection system is notonly useful to detect a telephone conversation but can also readily beused to prepare the hearing device when a telephone call is likely tooccur. This means that the telephone detection system is monitoring amomentary acoustic situation by applying specific criterions or socalled characteristic features, which give an indication on whether atelephone conversation is likely to occur.

The detection of a telephone conversation is in particular importantsince it allows the hearing device to operate in a hearing program thatis optimized for such an acoustic situation. Similarly, the predictionof a telephone conversation allows the hearing device to switch to ahearing program before the telephone conversation has started.Therewith, other acoustic signals that do not belong to the telephoneconversation can be eliminated.

The specific characteristic features, which are selected in order toperform the required task, form the basis in a signal detection processconducted in the hearing device. In fact, the signal detection processcombines different characteristic features to determine an overallprobability being indicative of a presence of audio information. Theaudio information can come from different source, such as, for example,the microphone built into or connected to the hearing device, or a socalled T-coil—again possibly incorporated into the hearing device—thatis used to pick up a magnetic field that contains the audio information.In a particular situation, a microphone as acoustic sensing means and aT-coil as magnetic sensing means are both provided. Usually, audioinformation of the acoustic sensing means are fed to a signal processingunit that performs the signal processing algorithms commonly implementedin a hearing device, while the magnetic sensing means provide a magneticaudio signal that is subject to the telephone detection process. As soonas, by applying the yet to describe characteristic features, audioinformation is detected in the input magnetic signal, the input acousticsignal presently processed in the signal processing unit is replaced bythe input magnetic signal. The input magnetic signal now contains therelevant audio information that is further processed in the signalprocessing unit, and, after the processing, is provided to the user ofthe hearing device.

A telephone situation (conversation, prediction) will cause severalcharacteristic effects. Any of those characteristic effects may becaused by situations other than a telephone conversation. The aim is todetect a combination of those characteristic effects. For example, anacoustic characteristic effect is the limited bandwidth of telephonespeech. Therefore, a first characteristic feature is the bandwidth thatis monitored. Although the sole monitoring of the bandwidth is notsufficient to reliably detect a telephone conversation. In addition, itmust be taken into account that the bandwidth is not limited when theuser of the hearing device is talking because the own voice is not bandlimited. In this case, the monitoring of an additional characteristicfeature may be necessary in order to reliably detect the telephoneconversation or the audio information in the input magnetic signal.

Further characteristic features are the following, for example:

-   -   Detection of a dial tone that usually is at 425 Hz;    -   Behavior of a feedback canceller present in the hearing device        is observed: an object that is close to the hearing device must        result in a change in the feedback filter coefficients;    -   Detection of a magnetic field that is close to the microphone.

The number and the kind of characteristic features is not limited. Infact, the more characteristic features are taken into account, thebetter the result of the detection of a telephone conversation will be.

In one embodiment of the present invention, a state machine is used tocombine all the characteristic features in order to determine theprobability for a telephone conversation at any point in time.

FIG. 1 shows an overview of such a telephone detection system in a blockdiagram. The characteristic features which are to be monitored can beseen on the lower level of the block diagram, according to which thecharacteristic features as the bandwidth, the dial tone, the feedbackcanceller and the activity of the T-coil is monitored. The results ofthe monitoring of the characteristic features are provided as inputsignals to a so called top-level model by that an overall telephoneprobability is determined. The top-level model is implemented as a socalled state machine, for example.

The characteristic features as mentioned above are further described inmore detail in the following:

Classifier Telephone Feature

Telephone speech is typically limited to a bandwidth of 3 kHz. An inputsignal with such a bandwidth can be detected.

Dial Tone

The telephone dial tone has an international standard pitch of 425 Hz.The dial tone having consecutive tones of this frequency can thereforebe detected.

Feedback Canceller: Object Detection

The feedback canceller contains an adaptive filter that follows thefeedback path from receiver to the microphone of a hearing device. Thefeedback path can change dramatically if an object is brought close tothe ear with the hearing device. By monitoring the behavior of thefilter of the feedback canceller, it is possible to detect when anobject, such as a telephone, is close to the microphone of the hearingdevice.

T-Coil

The T-Coil detects a magnetic field near the hearing device. If themagnetic field strength reaches a certain threshold a switch isactivated. This can be used as an additional characteristic feature.

It has already been mentioned that the top-level model is, according toone embodiment, implemented as a state machine. Such as state machine isdepicted in FIG. 2 and has four states.

The purpose of the state machine is to combine the results of monitoringthe characteristic features to determine the overall possibility of atelephone conversation. In one embodiment, the state machine has fourstates as follows:

-   -   1. Idle    -   2. Dial Tone    -   3. Listen    -   4. Speak

These four states correspond to the situations the hearing device can bein. The default state is “Idle”, during which the hearing device is in anormal hearing situation. The last three states correspond to atelephone situation. During a telephone conversation the user can beeither speaking or listening, or can be listening to a dial tone at thebeginning of a conversation. At any point in time m, every state has acertain probability associated to it that indicates how likely it isthat the hearing device is in the corresponding acoustic situation. Thesum of all states is always equal to 1. The four probabilities areexpressed as a vector:P _(Total)(m)=[p _(Idle) p _(DialTone) p _(Listen) p _(Speak)]

The overall telephone probability is the sum of the states two, threeand four, i.e.P _(Telephone) =p _(DialTone) +p _(Listen) +p _(Speak)

Similarly, every characteristic feature has associated to it afour-element probability vector. The probabilities in the vector changeaccording to whether the characteristic feature changes or not. Forexample, if the “Dial Tone” characteristic feature is detected, itsprobability vector will have a high probability for the “Dial Tone”state and a low probability for every other state.

At every point in time, the probability vector is updated. The updateoccurs according to the newest input from the characteristic featuremonitoring and the transition probabilities between the states (p_(xy)in FIG. 2). The transition probabilities are a design parameter andremain fixed during operation. Since there are four states, thetransition probabilities can be written in a four-by-four matrix Aaccording to:

$A = \begin{bmatrix}p_{11} & p_{12} & p_{13} & p_{14} \\p_{21} & p_{22} & p_{23} & p_{24} \\p_{31} & p_{32} & p_{33} & p_{34} \\p_{41} & p_{42} & p_{43} & p_{44}\end{bmatrix}$

Every element of the matrix indicates the probability of a transitionbetween two states. For example, p₁₂ denotes the probability of atransition from state 1 to state 2, p₃₁ a transition from state 3 tostate 1, and so on.

In FIG. 3, a hearing device according to the present invention isdepicted. The hearing device comprises a microphone 1, a signalprocessing unit 2, a loudspeaker 3, a T-coil 5, two analog-to-digitalconverters 4 and 6 and a digital-to-analog converter 7. The signalprocessing unit 2 comprises a telephone detection unit 9, a switchingunit 10 and an information processing unit 8. The microphone 1 is anacoustic sensing unit for sensing an acoustic signal and for providingan input acoustic signal to the analog-to-digital converter 4 that isconnected to the signal processing unit 2. The T-coil 5 is a magneticsensing unit for sensing a magnetic signal and for providing an inputmagnetic signal to the analog-to-digital converter 6 that is alsoconnected to the signal processing unit 2. In the signal processing unit2, an information signal is determined based on the input acousticsignal and the input magnetic signal, the information signal beingprocessed in the information processing unit 8, which provides an outputsignal to a user of the hearing device via digital-to-analog converter 7and loudspeaker 3.

In accordance with the telephone detection process described above, thetelephone detection unit 9 monitors the input magnetic signal providedby the T-coil 5. Basically, the telephone detection unit 9 monitors thecharacteristic features described in connection with the telephonedetection process, i.e. as soon as a determined probability reaches apredetermined threshold level indicating that a telephone conversationis most likely or indicating that a telephone call is most likely tohappen, the switching unit 10 is activated in such a manner that theinput magnetic signal is fed to the information processing unit 8, inwhich algorithms to improve the hearing of the hearing device user areapplied. In fact, the input signal to the information processing unit8—also called the information signal—is equal to the input acousticsignal in cases were the determined probability lies below thepredetermined threshold, and is equal to the input magnetic signal incases were the determined probability is equal to the predeterminedthreshold or lies above the predetermined threshold.

Having discloses the structure of an implementation of the inventivehearing device, it is noted that some of the tasks which have beenassigned to individual blocks in the block diagram of FIG. 3, canreadily implemented as software routines performing the assigned task.In particular, the telephone detection unit 9 could also be seen asmeans implementing the telephone detection process described inconnection with the inventive method.

In a further embodiment of the present invention, the telephonedetection unit 9 is incorporated into the signal path carrying the inputacoustic signal, and not into the signal path carrying the inputmagnetic signal as shown in FIG. 3. Accordingly, this embodiment of thepresent invention allows to base the telephone detection process on theinput acoustic signal, which is advantageous in cases were no or only aweak input magnetic signal can be received.

Although a T-coil 5 is disclosed in the various embodiments shown above,other methods or devices can be used for transmitting a telephone signalto the hearing device. Other than a magnetic transmission, as forexample it is the case with a T-coil, a transmission via Bluetooth orother transmission protocols can also be used.

1. A method of operating a hearing device, the method comprising thesteps of: sensing an acoustic signal and providing an input acousticsignal, sensing a magnetic signal and providing an input magneticsignal, selecting one of the input acoustic signal and the inputmagnetic signal as an information signal, wherein the input magneticsignal is selected as the information signal after a signal detectionprocess has determined a probability being above a preset value, saidprobability being indicative of a presence of audio information in theinput magnetic signal, and processing the information signal andproviding an output signal to a user of the hearing device, wherein theprobability is determined by monitoring a bandwidth of the inputmagnetic signal and by monitoring at least one of the followingcriterions: presence of a telephone dial tone; behavior of a feedbackcanceller filter indicating an object being close to an ear; and amagnetic field is present in a T-coil.
 2. The method of claim 1, whereinthe step of selecting one of the input acoustic signal and the inputmagnetic signal as the information signal is performed using a statemachine.
 3. The method of claim 2, wherein the state machine comprisesat least four states comprising: an Idle state being a default state; anDialTone state being representative for detecting dial tone; a Listenstate being representative for receiving acoustic information from aremote person talking via telephone; a Speak state being representativefor speaking to a remote person via telephone.
 4. A method of operatinga hearing device, the method comprising the steps of: sensing anacoustic signal and providing an input acoustic signal, sensing amagnetic signal and providing an input magnetic signal, selecting one ofthe input acoustic signal and the input magnetic signal as aninformation signal, wherein the input acoustic signal is selected as theinformation signal after a signal detection process has determined aprobability being above a preset value, said probability beingindicative of a presence of audio information in the input acousticsignal, and processing the information signal and providing an outputsignal to a user of the hearing device, wherein the probability isdetermined by monitoring a bandwidth of the input acoustic signal and bymonitoring at least one of the following criterions: presence of atelephone dial tone; behavior of a feedback canceller filter indicatingan object being close to an ear; and a magnetic field is present in aT-coil.
 5. The method of claim 4, wherein the step of selecting one ofthe input acoustic signal and the input magnetic signal as theinformation signal is performed using a state machine.
 6. The methodclaim 5, wherein the state machine comprises at least four statescomprising: an Idle state being a default state; an DialTone state beingrepresentative for detecting dial tone; a Listen state beingrepresentative for receiving acoustic information from a remote persontalking via telephone; a Speak state being representative for speakingto a remote person via telephone.
 7. A hearing device comprising: anacoustic sensor for sensing an acoustic signal and providing an inputacoustic signal, a magnetic sensor for sensing a magnetic field signaland providing an input magnetic signal, a telephone detection unitconnected to the magnetic sensor for selecting one of the input acousticsignal and the input magnetic signal as an information signal, whereinthe telephone detector unit selects the input magnetic signal as theinformation signal after a telephone detection process has determined aprobability being above a preset value, said probability beingindicative of a presence of audio information in the input magneticsignal, and an information processing unit for processing theinformation signal to a user of the hearing device, wherein theprobability is determined by monitoring a bandwidth of the inputmagnetic signal and by monitoring at least one of the followingcriterions: presence of a telephone dial tone; behavior of a feedbackcanceller filter indicating an object being close to an ear; and amagnetic field is present in a T-coil.
 8. The hearing device of claim 7,further comprising a switch unit for operationally connecting either themagnetic sensor or the acoustic sensor to the information processingunit, the switch unit being controllable by the telephone detectionunit.
 9. The hearing device of claim 7, further comprising a statemachine in the telephone detection unit.
 10. The hearing device of claim8, further comprising a state machine in the telephone detection unit.11. The hearing device of one of the claim 9 or 10, wherein the statemachine comprises at least four states comprising: an Idle state being adefault state; an DialTone state being representative for detecting dialtone; a Listen state being representative for receiving acousticinformation from a remote person talking via telephone; and a Speakstate being representative for speaking to a remote person viatelephone.
 12. A hearing device comprising: an acoustic sensor forsensing an acoustic signal and providing an input acoustic signal, amagnetic sensor for sensing a magnetic field signal and providing aninput magnetic signal, a telephone detection unit connected to theacoustic sensor for selecting one of the input acoustic signal and theinput magnetic signal as an information signal, wherein the telephonedetector unit selects the input acoustic signal as the informationsignal after a telephone detection process has determined a probabilitybeing above a preset value, said probability being indicative of apresence of audio information in the input acoustic signal, and aninformation processing unit for processing the information signal to auser of the hearing device, wherein the probability is determined bymonitoring a bandwidth of the input acoustic signal and by monitoring atleast one of the following criterions: presence of a telephone dialtone; behavior of a feedback canceller filter indicating an object beingclose to an ear; and a magnetic field is present in a T-coil.
 13. Thehearing device of claim 12, further comprising a switch unit foroperationally connecting either the magnetic sensor or the acousticsensor to the information processing unit, the switch unit beingcontrollable by the telephone detection unit.
 14. The hearing device ofclaim 12, further comprising a state machine in the telephone detectionunit.
 15. The hearing device of claim 13, further comprising a statemachine in the telephone detection unit.
 16. The hearing device of oneof the claim 14 or 15, wherein the state machine comprises at least fourstates comprising: an Idle state being a default state; an DialTonestate being representative for detecting dial tone; a Listen state beingrepresentative for receiving acoustic information from a remote persontalking via telephone; and a Speak state being representative forspeaking to a remote person via telephone.